Explain an alpha channel and how alpha channels are used. Also explain what the similarities are between alpha channels and new layers/layer masks, as well as the differences between them.

Question

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Answer 1

When you create a new channel, by default it becomes an alpha channel. An alpha channel, or alpha channel mask, is a special channel that saves and loads selection marquees. It is similar to a new layer or layer mask in that it is used to edit or mask parts of an image. Alpha channel masking can be performed on the background layer, whereas masks created using the Layers panel cannot. Alpha channels represent selections and exist independently of any particular layer — for that reason, storing selections as alpha channels creates more permanent masks than layer masks. You can reuse the stored selections or even load them into another image. The Channel Options command on the panel menu allows you to name the alpha channel and adjust settings related to editing.

Most commonly, alpha channels are used to isolate and protect areas of an image as you apply color changes, filters, or other effects to the rest of the image. Additionally, alpha channels are used for complex image editing, such as gradually applying color or filter effects to an image. For instance, viewing an alpha channel and the composite channel together allows you to see how changes made in the alpha channel relate to the entire image. When you display an alpha channel at the same time as a color channel, the alpha channel appears as a transparent color overlay in the document window.